The present invention is directed to a bowler's device for aiding the bowler in keeping his arm straight when rolling the ball during delivery, in order to increase the accuracy by which the bowling ball is rolled down an alley. The device of the present invention may also be used in any sport where it is desired to keep at least one arm of the sportsman as straight as possible, such as, for example, in golfing, where the arm closest to the fairway must be kept as straight as possible during the forward portion of the swing. The device of the present invention may also be used by a tennis player in the same manner, and may be used to instruct and teach a novice in the sport, by habituating him to keep his arm straight, in the proper manner. Aiding devices for keeping a bowler's arm straight are known, and have been used also for other sports, as well as for use as an orthopedic brace. However, all such prior-art locking devices require the user thereof to manually manipulate the locking device to allow for the bending of the arm to which the device is secured. Thus, whenever a user of these prior-art devices desires to allow for the bending of his or her arm, the lock of the device must be manually released either by using the other, free arm, or by another person entirely. The problem with this manner of unlocking the arm-straightening device is that it cannot allow for follow-through of the arm after completing the arm-swing required. For example, in the sport of bowling, when it is necessary to keep the arm straight during approach to the alley and during the back-swing and for most of the forward-swing of the arm, it is also necessary to allow for the arm to follow-through in order to impart sufficient rotation to the ball to allow for a hooked-path of travel thereof down the alley. The spin thus given to the ball causes it to take a curved path, which has long been known as increasing pin-action, leading to higher scores. Further, by allowing the arm to bend at the end-point of delivery, greater accuracy is achieved when aiming the ball at a chosen arrow on the alley. Hitherto, prior-art arm-locking devices have not allowed any bending of the arm at the end of delivery, thus preventing proper and effective follow-through. The same principal applies also for other sports, such as golf and tennis, where a follow-through is necessary after the hitting of the ball. It is, therefore, advantageous to provide an arm-straightening device for sportsmen that also allows for the automatic bending of the arm at a certain stage during delivery to provide for proper and correct follow-through.